Piston for an internal combustion engine and method for its production

ABSTRACT

A method for the production of a piston for an internal combustion engine, having a piston head, a piston skirt, and a circumferential recess configured between the piston head and the piston skirt. The piston has a piston base body and a piston ring element. The piston base body has at least a crown region of a combustion bowl as well as the piston skirt. The piston ring element has at least a piston crown, a wall region of the combustion bowl, a circumferential top land, and a circumferential ring belt with ring grooves. The piston ring element has a circumferential cooling channel between the wall region of the combustion bowl and the ring belt, closed with a closure element. The piston base body and the piston ring element are connected by a circumferential joining seam in the region of the combustion bowl.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 13/066,560,filed on Apr. 18, 2011, which claims priority under 35 U.S.C. 119 ofGerman Application No. 10 2011 013 113.2 filed on Mar. 4, 2011, thedisclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a piston for an internal combustionengine, having a piston head, a piston skirt, and a circumferentialrecess configured between the piston head and the piston skirt. Thepresent invention furthermore relates to a method for the production ofsuch a piston.

A piston of this type is known, for example, from DE 44 46 726 A1, andis also referred to as a “piston having a thermally uncoupled pistonskirt.” Such pistons are characterized by great strength and by greatheat resistance, because of the thermal uncoupling of piston head andpiston skirt. Their relatively great construction height, which resultsfrom a minimum height of the ring-shaped recess, required due to processtechnology, is disadvantageous.

SUMMARY OF THE INVENTION

The task of the present invention consists in further developing apiston of the stated type, in such a manner that the construction heightis reduced, while the good mechanical and thermal properties remain thesame.

The solution consists in that the piston has a piston base body and apiston ring element, that the piston base body has at least a crownregion of a combustion bowl as well as the piston skirt, that the pistonring element has at least a piston crown, a wall region of thecombustion bowl, a circumferential top land, and a circumferential ringbelt provided with ring grooves, that the piston ring element has acircumferential cooling channel between the wall region of thecombustion bowl and the ring belt, closed with a closure element, thatthe piston base body and the piston ring element have a circumferentialjoining seam in the region of the combustion bowl, by way of which seamthey are non-releasably connected with one another.

Furthermore, an object of the invention is a method for the productionof such a piston, having the following method steps: (a) makingavailable a blank of a piston base body that has at least a crown regionof a combustion bowl, a piston skirt, as well as a joining surface inthe region of the combustion bowl; (b) making available a blank of apiston ring element that has at least a piston crown, a wall region ofthe combustion bowl, a circumferential recess, as well as a joiningsurface in the region of the combustion bowl; (c) connecting the blankof the piston base body with the blank of the piston ring element by wayof their joining surfaces, to produce a piston blank; (d) reworkingand/or finishing the piston blank to produce the piston.

The idea according to the invention consists in providing a pistonhaving a thermally uncoupled piston skirt with a piston ring elementconfigured as a separate component. The recess, which serves as acircumferential cooling channel in the finished piston, can be workedinto the piston ring element in any desired size and constructionheight, and thus in advance. This eliminates the need to configure thecircumferential recess, which brings about the thermal uncoupling of thepiston skirt, with such a large construction height that production ofthe cooling channel by means of chip-cutting machining, as known forpistons according to the state of the art, is made possible in the firstplace. The piston according to the invention therefore makes it possibleto freely select the height of the circumferential recess and thus theconstruction height, and to keep it as low as possible, if necessary.

Advantageous further developments are evident from the dependent claims.

A preferred further development consists in that the joining seamencloses an acute angle with the center axis of the piston. Thisconfiguration allows particularly simple use of a welding method forjoining the piston components. In the case of beam welding, for examplelaser welding, the direction of the exiting weld beads can be controlledin such a manner that they remain outside of the cooling channel and donot impact the closure element.

It is practical if the closure element is held on the piston ringelement in the region of the ring belt. This configuration allowsparticularly simple installation of the closure element.

Particularly preferably, the end of the joining seam on the coolingchannel side lies outside of the cooling channel. In this manner,depending on the joining method used, material residues such as weldridges that might be present are removed in simple manner. Furthermore,it is avoided that such material residues constrict or contaminate thecooling channel.

Another particularly preferred embodiment consists in that the free edgeof the closure element is disposed above the joining seam. Thisembodiment allows already closing the recess in the blank of the pistonring element, before it is connected with the blank of the piston basebody. This is particularly advantageous if the blanks of the piston ringelement and of the piston base body are to be connected with one anotherby means of beam welding, particularly laser welding. The weld beadsthat occur during this joining method cannot get into the coolingchannel during the joining process in this case, and constrict orcontaminate it. In this case, the closure element can also bepermanently attached in the region of the ring belt even before joining.However, the closure element can also be reversibly or interchangeablyaffixed before joining, and, for example in the case of contaminationwith weld beads, can be replaced with a clean closure element subsequentto the joining process.

Of course, the closure element can also be affixed to the piston onlyafter the joining process, forming the cooling channel.

The closure element is preferably configured as a one-piece ormulti-piece sheet-metal component. In the installed state, its free endcan lie against the piston, or be spaced apart from the piston in theform of a gap. The closure element can also be configured as a one-pieceor multi-piece spring sheet. Then the closure element can be attached tothe piston in such a manner that its free edge lies against the pistonunder bias, in order to close the cooling channel in particularly securemanner.

It is practical if the closure element has at least one entry openingand at least one exit opening for cooling oil. In this connection, theat least one inlet opening can have a sleeve-shaped guide element forthe cooling oil, which element projects into the cooling channel. Such aguide element can be formed into the closure element, for example,during its production.

The present invention is suitable for all piston construction variantsaccording to the claims. The piston base body or its blank can also havepart of the wall region, aside from the crown region of the combustionchamber bowl.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention will be explained ingreater detail below, using the attached drawings. These show, in aschematic representation, not true to scale:

FIG. 1 an exemplary embodiment of a piston according to the invention,in section;

FIG. 2 the piston according to FIG. 1, in section, in a representationrotated by 90°;

FIG. 3 an enlarged representation of the piston ring element of thepiston according to FIG. 1, having a closure element;

FIG. 4 an enlarged representation of a collar in the closure elementaccording to FIG. 3;

FIG. 5 an exemplary embodiment of a blank of a piston ring element for apiston according to the invention, in section;

FIG. 6 an exemplary embodiment of a blank of a piston base body for apiston according to the invention, in section;

FIG. 7 the blank of a piston ring element according to FIG. 5, with aclosure element attached to it;

FIG. 8 a piston blank composed of the components according to FIGS. 6and 7.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIGS. 1 and 2 show a particularly preferred exemplary embodiment of apiston 10 according to the invention. The piston 10 has a piston basebody 11 and a piston ring element 12. Both components can consist of anydesired metallic material that is suitable for joining the components.The piston base body 11 and the piston ring element 12 together form thepiston head 10 a and the piston skirt 15 of the piston 10.

The piston base body 11 has a piston skirt 15 that is provided, in knownmanner, with pin bosses 16 and pin bores 17 for accommodating a pistonpin, as well as with working surfaces 18. The piston ring element 12 hasa piston crown 21 as well as a circumferential top land 22 and acircumferential ring belt 23 for accommodating piston rings.

The piston 10 or the piston head 10 a is furthermore provided with acombustion bowl 19. In this connection, the piston base body 11 has acrown region 19 a of the combustion bowl 19, while the piston ringelement 12 has a wall region 19 b of the combustion bowl 19.

The pin bosses 16 of the piston base body 11 are suspended on theunderside of the crown region 19 a of the combustion bowl 19 by way ofpin boss links 24. The piston skirt 15 is separated from the ring belt23 by means of a circumferential, ring-shaped recess 25. Thus, thepiston skirt 15 is thermally uncoupled from the piston head 10 a.

The piston ring element 12 has a circumferential cooling channel 27,closed with a closure element 26, between the wall region 19 b of thecombustion bowl 19 and the ring belt 23.

The piston base body 11 and the piston ring element 12 are connectedwith one another by means of joining, in the exemplary embodimentpreferably by means of laser welding. As a result, a joining seam 28 isformed in the region of the combustion bowl 19, which seam encloses anacute angle a with the center axis M of the piston 10 in thisparticularly preferred exemplary embodiment.

The configuration of the piston 10 according to the invention, with apiston base body 11 and a piston ring element 12, makes it possible toform the recess 27 a that forms the subsequent cooling channel 27 intothe piston ring element 12 in advance, in any desired size andconstruction height. This eliminates the need to configure thecircumferential recess 25, which brings about thermal uncoupling of thepiston skirt 15 from the piston head 10 a, with such a largeconstruction height that production of the cooling channel by means ofchip-cutting machining, as known for pistons according to the state ofthe art, is made possible in the first place. The piston 10 according tothe invention therefore makes it possible to keep the height of thecircumferential recess 25 and thus the construction height, as shown inFIG. 1, as low as possible.

FIG. 3 shows an enlarged detail picture of the piston ring element 12 ofthe piston 10 according to FIG. 1. In the particularly preferredexemplary embodiment shown, the cooling channel 27 is closed by means ofa closure element 26. The closure element 26 can be configured in onepiece or in multiple pieces. The closure element 26 is attached to theunderside of the ring belt 23 of the piston ring element 12, in theexemplary embodiment, by means of weld points 29. Of course, the closureelement 26 can be connected with the piston 10 by means of any otherdesired methods. The free edge 26 a of the closure element 26 lies onthe back of the wall region 19 b of the combustion bowl 19 of the pistonring element 12 in the exemplary embodiment. The free edge 26 a of theclosure element 26 can also be spaced apart from the back of the wallregion 19 b of the combustion bowl in the form of a gap. If the closureelement 26 is configured as a spring sheet, its free edge 26 a can alsolie against the back of the wall region 19 b of the combustion bowl 19under bias.

This particularly preferred embodiment of the piston 10 according to theinvention includes that the end 28 a of the joining seam 28, on thecooling channel side, lies outside of the cooling channel 27. Thismeasure makes it possible to already attach the closure element 26 tothe blank of the piston ring element 12 even before it is connected withthe blank of the piston base body 11. This allows particularly simpleuse of a welding method for joining the piston components, preferably abeam welding method, particularly preferably a laser welding method. Theweld beads that occur during these joining methods cannot enter into thecooling channel 27 during the joining process, in this case, andconstrict or contaminate the latter. The closure element 26 can alreadybe permanently attached to the blank of the piston ring element 12 evenbefore joining. However, the closure element 26 can also be reversiblyor interchangeably affixed before joining, and, for example in the caseof contamination with weld beads, replaced with a clean closure element26 subsequent to the joining process.

FIG. 4 shows another representation of the closure element 26 of thepiston 10. In this representation, it can be seen that the closureelement 26 has an entry opening 31 for cooling oil. The entry opening 31is provided with a sleeve-shaped guide element 32 that projects into thecooling channel 27 and serves, in known manner, to guide the cooling oilpassed into the cooling channel 27. The closure element 26 furthermorehas at least one exit opening for cooling oil (not shown), in knownmanner.

The piston 10 according to the invention is particularly preferablyproduced in the manner described below.

First, a pre-machined blank 11′ of a piston base body 11, in theexemplary embodiment, as well as a pre-machined blank 12′ of a pistonring element 12, in the exemplary embodiment, are made available,according to FIGS. 5 to 8.

The blanks 11′, 12′ essentially correspond to the finished piston basebody 11 and the finished piston ring element 12, respectively, so thatthe same structures are provided with the same reference symbols, andreference is made, in this regard, to the above description of FIGS. 1and 2. Two essential differences consist in that the pin bores 17 arenot structured in finished manner in the blank 11′ of the piston basebody 11, and that the ring grooves are absent in the blank 12′ of thepiston ring element 12.

Depending on the selection of the material, the blanks 11′, 12′ can becast, forged, or sintered by means of powder metallurgy. In theexemplary embodiment, the crown region 19 a of the combustion bowl 19 isformed into the blank 11′ of the piston base body 11. This results in acircumferential joining surface 33 that encloses the same acute angle awith the center axis M of the blank 11′, which is identical with thecenter axis M of the finished piston 10, that the joining seam 28 in thefinished piston 10 encloses with the center axis M.

In the exemplary embodiment, the wall region 19 b of the combustion bowl19 is formed into the blank 12′ of the piston ring element 12. Thisresults in a circumferential joining surface 34 that encloses the sameacute angle a with the center axis M of the blank 12′, which isidentical with the center axis M of the finished piston 10, that thejoining seam 28 in the finished piston 10 encloses with the center axisM.

The joining surfaces 33, 34 of the blank 11′ of the piston base body 11or of the piston blank 12′ of the piston ring element 12, respectively,correspond with one another in such a manner that the blanks 11′, 12′can be joined together to produce a piston blank 10′ (see FIG. 8).

In the exemplary embodiment, the recess 27 a provided in the blank 12′of the piston ring element 12 is closed with a closure element 26 in theform of a metal sheet, forming a cooling channel 27 (see FIG. 7). Themetal sheet can be in one piece or multiple pieces; furthermore, a plainmetal sheet or a spring sheet can be used. The closure element 26 isattached on the underside of the ring belt 23 of the blank 12′ of thepiston ring element 12, in the exemplary embodiment, by means of weldpoints 29. The free edge 26 a of the closure element 26 is positioned onthe back of the wall region 19 b of the combustion bowl 19 of the pistonblank 12′ of the piston ring element 12, in the exemplary embodiment.The free edge 26 a of the closure element 26 can lie against the back ofthe wall region 19 b, but can also be spaced apart from the back of thewall region 19 b, in the form of a gap. If a spring sheet is used as theclosure element 26, the free edge 26 a can also lie against the back ofthe wall region 19 b under bias.

Of course, the closure element 26 can also be releasably connected withthe blank 12′ of the piston ring element 12 and removed again after thejoining process (see below).

Subsequent to this, the blank 11′ of the piston base body 11 and theblank 12′ of the piston ring element 12 are connected by way of thejoining surfaces 33, 34, in non-releasable manner, to form a pistonblank 10′ (see FIG. 8).

The exemplary embodiment of the piston 10 according to the inventionshown here, and the production method according to the invention,respectively, allow connecting the blanks 11′, 12′ with one another bymeans of beam welding, particularly laser welding, in particularlyadvantageous manner. The weld beads that occur during this joiningmethod cannot get into the cooling channel 27 during the joiningprocess, and constrict or contaminate the latter, since the coolingchannel 27 is permanently or releasably closed by means of the closureelement 26. In the latter case, the closure element 26 can be replacedwith a clean closure element 26, for example in the event ofcontamination with weld beads, subsequent to the joining process. Sincethe joining surfaces 33, 34 furthermore enclose an acute angle a withthe center axis M of the blanks 11′, 12′, the direction of the weldbeads that exit during beam welding can be controlled in such a mannerthat they remain outside of the cooling channel 27. The weld beads canimpact on the closure element 26, for example, which can subsequently bereplaced, if necessary. However, the weld beads can also exit into theopen or impact on the inside of the piston skirt, where they eitherremain or can be removed during the course of known reworking.

Since the end 28 a of the joining seam 28 on the cooling channel sidelies outside of the cooling channel 27 in the particularly preferredembodiment, any material residues such as weld ridges can be easilyremoved, if necessary, depending on the joining method used.Furthermore, it is avoided that such material residues constrict orcontaminate the cooling channel 27.

Of course, the closure element 26 can also be affixed to the piston 10only after the joining process, forming the cooling channel 27.

The piston blank 10′ is reworked or finished in known manner, dependingon the configuration of the blanks 11′, 12′. For example, the outershape, surfaces, combustion chamber bowl, ring belt, pin bores, etc. canbe finished. In the end result, the piston 10 described above, accordingto FIGS. 1 and 2, is obtained.

In the end result, a piston 10 having an uncoupled skirt is obtained,whose circumferential recess 25, which brings about the thermaluncoupling of the piston skirt, can be produced with a freely selectableconstruction height, which is kept as low as possible, if necessary.

What is claimed is:
 1. A method for the production of a piston for aninternal combustion engine, the piston having a piston base body and apiston ring element and a ring-shaped recess configured between a pistonhead and a piston skirt, the method comprising the following steps: (a)making available a blank of a piston base body that has at least a crownregion of a combustion bowl, the piston skirt, as well as a joiningsurface in a region of the combustion bowl; (b) making available a blankof a piston ring element that has at least a piston crown, a wall regionof a combustion bowl, a circumferential recess, as well as a joiningsurface in the region of the combustion bowl; (c) connecting the blankof the piston base body with the blank of the piston ring element by wayof their joining surfaces, to produce a piston blank; and (d) reworkingor finishing the piston blank to produce the piston.
 2. The methodaccording to claim 1, wherein subsequent to step (b) or subsequent tostep (c), the recess is closed by a closure element, so that acircumferential cooling channel is formed.
 3. The method according toclaim 2, wherein subsequent to step (b), the closure element isreversibly or irreversibly attached in a region of the ring belt.
 4. Themethod according to claim 1, wherein the joining surfaces enclose anacute angle (a) with the center axis (M) of the piston.
 5. The methodaccording to claim 1, wherein the blanks of piston base body and pistonring element are connected with one another by beam welding.
 6. Themethod according to claim 1, wherein the blank of the piston base bodyhas at least the crown region and a part of the wall region of thecombustion bowl.
 7. A piston produced according to a method of claim 1.